Look at the family history of the Flynn-Fletcher..., most of them have alike head, and or other forms of an identical body. That is... all except Phineas. Linda's parents, nor Candace and Linda, have a Triangular Shaped head. So could they be his true parents? Ferb's head resembles his Father, and Granpa. Linda resembles her mother, and so does Candace. Lawrence resembles his father, but Phineas is the odd one out. Weird...